Keep the selection of the text field when changed by JS.

Source/core/input/EventHandler.cpp

Index: Source/core/input/EventHandler.cpp
diff --git a/Source/core/input/EventHandler.cpp b/Source/core/input/EventHandler.cpp
index 3788a52df2b13812b6a69145673453db57c674ac..314c6a382d0c34a25fb4ec22f16e39bb30c9f3cb 100644
--- a/Source/core/input/EventHandler.cpp
+++ b/Source/core/input/EventHandler.cpp
@@ -362,7 +362,6 @@ bool EventHandler::handleMousePressEvent(const MouseEventWithHitTestResults& eve
 
     bool swallowEvent = false;
     m_mousePressed = true;
-    selectionController().initializeSelectionState();
 
     if (event.event().clickCount() == 2)
         swallowEvent = selectionController().handleMousePressEventDoubleClick(event);
@@ -950,6 +949,10 @@ bool EventHandler::handleMousePressEvent(const PlatformMouseEvent& mouseEvent)
     m_frame->selection().setCaretBlinkingSuspended(true);
 
     bool swallowEvent = !dispatchMouseEvent(EventTypeNames::mousedown, mev.innerNode(), m_clickCount, mouseEvent, true);
+    // m_selectionInitiationState is initialized after dispatching mousedown event in order not to keep the selection by DOM APIs

[yosin_UTC9, 2015/07/06 01:57:30]

nit: Could you try to keep comments in 80 chars? It makes some tools happy, e.g.
codereview.chromium.org, git log and so on.

[Miyoung Shin(g), 2015/07/13 03:32:57]

Done.

+    // Because we can't give the user the chance to handle the selection by user action like dragging if we keep the selection in case of mousedown.
+    // FireFox also has the same behavior and it's more compatible with other browsers.
+    selectionController().initializeSelectionState();
     HitTestResult hitTestResult = hitTestResultInFrame(m_frame, mouseEvent.position(), HitTestRequest::ReadOnly);
     swallowEvent = swallowEvent || handleMouseFocus(MouseEventWithHitTestResults(mouseEvent, hitTestResult));
     m_capturesDragging = !swallowEvent || mev.scrollbar();
@@ -2021,6 +2024,7 @@ bool EventHandler::handleGestureTap(const GestureEventWithHitTestResults& target
         static_cast<PlatformEvent::Modifiers>(modifiers | PlatformEvent::LeftButtonDown),
         PlatformMouseEvent::FromTouch,  gestureEvent.timestamp());
     bool swallowMouseDownEvent = !dispatchMouseEvent(EventTypeNames::mousedown, currentHitTest.innerNode(), gestureEvent.tapCount(), fakeMouseDown, true);
+    selectionController().initializeSelectionState();
     if (!swallowMouseDownEvent)
         swallowMouseDownEvent = handleMouseFocus(MouseEventWithHitTestResults(fakeMouseDown, currentHitTest));
     if (!swallowMouseDownEvent)